• The faceplate of the thing (which is a lovely brass colour) is engraved with a ‘this way to undo arrow’ so that’s the way this is removed?

    That's the way that plate is removed (it's the outer cone of the freewheel bearing): it has a left hand thread. The block itself has a righthand thread onto the hub - otherwise it would unscrew under pedal pressure!

    If you hope to re-use the block you will have to find a removing tool that is a near perfect fit to those slots. Any old established bike shop should have one.

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